Diode pumped solid state opto-mechanically optimized green laser

ABSTRACT

A unique physical design of 532 nm Diode Pumped Solid State (DPSS) laser elements to achieve independent crystal phasing (rotation), spacing and output coupler (OC) alignment in a robust small package is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority from U.S. Provisional Patent Application No. 61/561,335 filed on Nov. 18, 2011, by R. Battis, et al. titled “GREENSTAR II™—DPSS OPTO-MECHANICALLY OPTIMIZED GREEN LASER.” This application is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention concerns laser apparatus. More particularly, the invention concerns diode pumped solid state (“DPSS”) lasers and design of laser elements to achieve independent crystal phasing, spacing and output coupler alignment.

BACKGROUND OF THE INVENTION

Diode pumped solid state lasers are used in industry to provide an inexpensive yet powerful laser source. In applications, it is often desirable to convert the wavelength of the laser light produced by the laser diode to a different wavelength. This traditionally entails the use of one or more crystals and an output coupler aligned for phasing and cavity tuning i.e., rotation and spacing relative to the laser diode.

For example, in one DPSS laser system, it is desirable to convert a laser diode output at 808 nm to a 532 nm green laser. This may be done by passing the output light through first a Nd:YVO4 crystal to convert the light to 1064 nm, and then passing it through a KTP crystal to convert to the desired 532 nm laser, which then would exit through an output coupler. In order to maintain acceptable output quality and intensity, it is advantageous to optimize the phasing or “rotation” and distance of the Nd:YVO4 crystal with respect to the laser diode, as well as that of the KTP crystal with respect to the Nd:YVO4 crystal and the output coupler with respect to the KTP and Nd:YVO4 crystals. It would also be useful to provide for pitch and yaw control of the KTP and output coupler as well.

In a traditional arrangement, the Nd:YVO4 and KTP crystals are typically packaged in mounts which are fixed into optimal positions in rotation and distance using shunts and glue. This approach has several drawbacks. For example, if the positioning of the shunts is shifted, such as by a shock to the device in which the laser is mounted, laser output can be adversely affected and a repair would require dismantling and replacing the shunts, which may further damage the device.

Also, in traditional lasers, the crystals and other elements typically cannot be independently aligned for crystal rotation, pitch and yaw adjustment and X-Y-Z orthogonal adjustments.

It is thus desirable to provide a physical design of a DPSS laser where the elements can be provided in a small compact package that incorporates precision techniques for aligning all electro-optic elements, to include crystal rotation, pitch and yaw adjustments and X-Y-Z orthogonal adjustments.

SUMMARY OF THE INVENTION

An aspect of the invention provides a laser apparatus including a laser diode, an Nd:YVO4 crystal, a KTP crystal, and an output coupler. The laser diode, Nd:YVO4 crystal, KTP crystal, and output coupler are aligned in order in an assembly to provide an optical path.

In an aspect of the invention, the Nd:YVO4 crystal is held at a predetermined distance from the laser diode on an adjustable rotating mount, the predetermined distance maintained by a spacer. The adjustable rotating mount and spacer together form an Nd:YVO4 assembly. The the Nd:YVO4 crystal is optimally rotated to a position to maximize output of the laser diode through the Nd:YVO4 crystal to produce 1064 nm radiation, the position fixed by a plurality of adjustment screws attached to the adjustable rotating mount.

In another aspect of the invention, the laser apparatus further provides for the KTP crystal to be held at a second predetermined distance from the Nd:YVO4 crystal on a second rotating mount. The second predetermined distance is maintained by a second spacer, the second rotating mount and second spacer having a plurality of rods and nuts fastened thereto for adjusting the pitch and yaw of the KTP crystal. In one embodiment, the second spacer includes a plurality of spring loaded adjustment screws for adjusting the second predetermined distance.

In various embodiments of the invention, the Nd:YVO4 crystal and KTP crystal may each be mounted in a one or two part mount.

Another aspect of the invention provides that the laser apparatus includes an output coupler held by an output coupler assembly. The output coupler assembly holds the output coupler at a third predetermined distance from the KTP crystal on a third pitch and yaw and Z adjustment mount, the third predetermined distance maintained by a third spacer. The third rotating mount and third spacer have rods and nuts fastened thereto for adjusting the pitch and yaw of the output coupler.

It is also provided that spring loaded adjustment screws may be used to provide for adjustment and locking into position of any or all of the Nd:YVO4 crystal, KTP crystal and/or output coupler.

Other forms of adjustable attachment, such as, but not limited to clips, slides, pins, and the like are also envisioned.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described with reference to the following drawing figures, in which like numerals represent like items throughout the figures, and in which:

FIG. 1 is a block diagram of an exemplary 532 nm diode pumped solid state (DPSS) laser that is useful for understanding the present invention.

FIG. 2 is a perspective view of an exemplary DPSS laser assembly that is useful for understanding the present invention.

FIG. 3 a is a perspective view of an exemplary 3 piece ND:YVO4 assembly that is useful for understanding the present invention.

FIG. 3 b is a perspective view of an exemplary 2 piece ND:YVO4 assembly that is useful for understanding the present invention.

FIG. 4 a is a perspective view of an exemplary 5 piece KTP assembly that is useful for understanding the present invention.

FIG. 4 b is a perspective view of an exemplary 4 piece KTP assembly that is useful for understanding the present invention.

FIG. 5 is a perspective view of an exemplary output coupler assembly that is useful for understanding the present invention.

DETAILED DESCRIPTION

The present invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operation are not shown in detail to avoid obscuring the invention. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.

The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is if, X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances.

The present invention advantageously provides physical designs of a diode pumped solid state (“DPSS”) laser where the elements can be provided in a small compact package that incorporates precision techniques for aligning all electro-optic elements, including crystal rotation, pitch and yaw adjustments and X-Y-Z orthogonal adjustments.

The present invention will be described here with reference to a DPSS 532 nm GREENSTAR(TM) laser by Laser Energetics, Inc. It is envisioned that the apparatus and techniques described herein may be useful in other laser devices.

A typical 532 nm solid state laser consists of the elements identified in FIG. 1, and in the order indicated. An 808 nm laser diode 100 is powered (power supply not depicted) to generate a laser output which is passed through a focusing/colliminating Doric lens 110. Next, the output light passes through a ND:YVO4 crystal 120 to convert the 808 nm laser light to 1064 nm. The 1064 nm light then passes through a KTP crystal 130 where it is converted to 532 nm for output through the output coupler 140.

The Laser Energetics, Inc.GreenStar™ II Diode Pumped Solid State (DPSS) laser is constructed using the elements of FIG. 1 in the assembly shown in FIG. 2. The optical coatings for the four optical elements are listed in Table 1, as one preferred embodiment of the laser/cavity design.

TABLE 1 Laser Element Coatings Element Input Coating (nm) Output coating (nm) Doric Lens [110] AR808 same ND:YV04 [120] AR808, HR532 AR1064, AR532 KTP [130] AR1064, AR532 AR1064, AR532 OC [140] HR1064, AR532 AR532 AR: Anti-Reflection coating HR: High Reflection coating

The exemplary compact design shown in FIG. 2 nests the elements of FIG. 1 in a unique and clever way to achieve optimal laser performance by incorporating alignment attributes of the ND:YV04 crystal, KTP crystal and OC as herein described.

As shown in FIG. 2, an embodiment of DPSS 532 nm laser incorporates a laser diode heat sink 200, upon which is mounted a platform 210 including a laser diode 100 and, optionally a Doric collimating lens 110. The collimating lens 110 may be provided as a separate component or as an integral part of the laser diode 100.

Attached to the platform 210 is the ND:YVO4 assembly 220, which includes a ND:YVO4 crystal 120 within The ND:YVO4 assembly 220 allows adjustments of distance and phase/rotation of the ND:YVO4 crystal 120 relative to the diode laser.

Attached to the ND:YVO4 assembly 220 is the KTP assembly 230, containing the KTP crystal 130, positioned with screws and springs 256 to allow pitch and yaw adjustment. The KTP assembly 230 allows independent rotation of the KTP crystal relative to the ND:YVO4 assembly 220. In an embodiment of the invention, the spacer 240 positioned above the KTP assembly is locked into position by nuts and rods 260 making its postion independent of the KTP assembly 230. The independent postioning of the spacer 240 allows independent positioning of the coupler (“OC”) assembly 250 relative to the KTP assembly 230. This independence is a critical feature of this invention. The OC assembly 250 preferably includes an output coupler 140 within In one embodiment of the invention, the OC assembly 250 is aligned and set in place using screws and springs 256.

Referring now to FIG. 3 a, in building a 532 mn DPSS laser, in one embodiment of the present invention using a 3 piece NH:YVO4 assembly 220, it is necessary to start with a 808 nm laser diode which is used as a pump of a Nd:YVO4 crystal. In this application it is critical to match the phase/rotational polarization of the 808 nm laser diode with the c axis—polarization—of the Nd:YVO4 crystal. This is achieved by a nesting a rotating mount 225 holding the Nd:YVO4 crystal 130 at a preferred distance 226 while allowing the optimal rotation to maximize the 808 nm diode through the Nd:YVO4 crystal, thus producing 1064 nm radiation which can be converted to the desired 532 mn output radiation through the follow-on elements.

In FIG. 3 b, an embodiment of the present invention using a 2 piece ND:YVO4 assembly is illustrated. The ND:YVO4 assembly 220 has been replaced by a ND:YVO4 mount 225 b with a built in distance adjuster/spacer. This embodiment has the advantage of fewer moving parts. In the design of FIG. 3 b the 360° rotation of the ND:YVO4 crystal is maintained but 226 ND:YV04 Distance Adjustor has been eliminated and 225 ND:YVO4 Mount has been redesigned as the 225 b ND:YV04 Mount to force a preset minimum height between the optional Doric lens and ND:YV04 crystal surface. The diameter of the 225 b ND:YV04 Mount over the 225 ND:YV04 Mount has been increased to mate with the hole in the 210 Platform. Rotation of the 225 b ND:YV04 Mount is accomplished using a standard pin tool pressing on the top serrated edge of the 225 b ND:YV04 Mount. Platform side set screws secure the 225 b ND:YV04 Mount final rotation position.

Referring now to FIG. 4 a, similar to the ND:YV04 crystal, the KTP crystal 130 which follows the ND:YV04 crystal, is provided the same adjustment capability via a KTP assembly 230 in rotation and distance, but independent of the ND:YV04. In addition, the KTP mount assembly 230 has a pitch and yaw capability through adjustment of the assembly securing nuts at different heights on the rods 260, FIG. 2.

The output coupler (OC) which follows the KTP crystal is housed in mount [255 FIG. 5] and rests on a spacer [240] which isolates the assembly [250] from the crystals below and gives it independent adjustment of spacing [256] as well as pitch and yaw [256].

In the design of FIG. 4 b, the 360° rotation of the KTP crystal 227 is maintained, as well as pitch and yaw control using the screws and springs 256 visible in FIG. 2. The KTP distance adjustor 229 has been eliminated and the ND:YV04 mount 228 has been redesigned as the mount 228 b to force a preset minimum height above the ND:YV04 crystal 130 below it. The diameter of the ND:YV04 mount 228 b over the ND:YV04 mount 228 has been increased to mate with the hole in the KTP assembly 230. Rotation of the KTP mount 228 b is accomplished using a standard pin tool pressing on the top serrated edge of the KTP mount 228 b. KTP assembly 230 side set screws secure the KTP mount 228 b final rotation position.

A further feature of the GreenStar™ II DPSS Laser is the ease of adjustment of the KTP and OC using springs force 256 and with the ability to lock-down their position for permanent alignment to resist vibration and shock in field use. Lock-down is accomplished by opposing forces of nuts and screws or just screws.

Referring now to FIG. 5, an exemplary OC assembly 250 is depicted. The OC assembly 250 incorporates an OC 140 as well as screws and springs 256 for adjusting the distance, pitch and yaw of the OC 140.

Having thus described the invention of the present application in detail and by reference to illustrative embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 

1. A laser apparatus comprising: a laser diode, an Nd:YVO4 crystal, a KTP crystal, and an output coupler, aligned in order in an assembly in an optical path; wherein the Nd:YVO4 crystal is held at a predetermined distance from the laser diode on an adjustable rotating mount, the predetermined distance maintained by a spacer, the adjustable rotating mount and spacer together forming an Nd:YVO4 assembly.
 2. The laser apparatus according to claim 1, wherein the a collimating lens is placed between the laser diode and the Nd:YVO4 crystal.
 3. The laser apparatus according to claim 1, wherein the laser diode incorporates a collimating lens.
 4. The laser apparatus according to claim 1, wherein the Nd:YVO4 crystal is optimally rotated to a position to maximize output of the laser diode through the Nd:YVO4 crystal to produce 1064 nm radiation, the position fixed by a plurality of adjustment screws attached to the adjustable rotating mount.
 5. The laser apparatus according to claim 4, wherein the KTP crystal is held at a second predetermined distance from the Nd:YVO4 crystal on a second rotating mount, the second predetermined distance maintained by a second spacer, the second rotating mount and second spacer having a plurality of rods and nuts fastened thereto for adjusting the pitch and yaw of the KTP crystal.
 6. The laser apparatus according to claim 5, further comprising the second spacer includes a plurality of spring loaded adjustment screws, wherein the second predetermined distance of the second spacer is adjusted using the spring loaded adjustment screws.
 7. The laser apparatus according to claim 5, wherein the output coupler is held by an output coupler assembly, the output coupler assembly holding the output coupler at a third predetermined distance from the KTP crystal on a third rotating mount, the third predetermined distance maintained by a third spacer, the third rotating mount and third spacer having a plurality of rods and nuts fastened thereto for adjusting the pitch and yaw of the output coupler, independent of the position of the KTP crystal.
 8. The laser apparatus according to claim 7, further comprising the third spacer includes a plurality of spring loaded adjustment screws, wherein the third predetermined distance of the third spacer is adjusted using the spring loaded adjustment screws. 